1. Field of the Invention
This invention relates to power source devices and, more particularly, to a power source device for supplying electric power to another device which is attachable to and detachable from the power source device.
2. Description of the Related Art
Conventionally, in the power source device to and from which a first device is attachable and detachable, as the means for controlling the supply of electric power to this first device, a system is known which, regardless of whether or not the first device is attached, supplies electric power at all times. Another system is known which operates in such a manner that, whether or not the first device is attached is mechanically detected by a switch or the like. Only when this device is being attached is the electric power supplied to the first device, while when the first device is not attached, the supply of the electric power to this device is stopped.
However, in such conventional examples as described above, with the former system that does the aforesaid supply of electric power regardless of whether or not the first device is attached, because the electric power is always supplied to the electric power supply terminals for the first device even when the first device is not attached, there is a possibility of occurrence of a short-circuiting if an electrically conductive object accidentally contacts across these terminals. This short-circuiting will be apt to cause damage to the power source device, or to destroy the safety device, such as fuse, of the power source device. In the case of the latter system that mechanically detects the presence or absence of the first device, concerning the above-described problem, a solution can be found that upon judgment of the fact that the first device is not attached, the electric power supply is stopped. Yet it also is accompanied with an alternative problem that the cost increases by the amount of the aforesaid detecting means.
With the first device in the normal attaching state, if it happens that the first device does not operate normally, then problems arise, particularly in a type of the first device which has elements that consume a relatively large amount of current at the start of movement thereof, for example, an electric motor, a plunger or the like. Also, if the first device has a microcomputer and other logic circuits as its control system and they malfunction such that normal control is not present, possibilities exist for damage to the first device, since as electric power is continually supplied thereto. The power source may also be consumed or its fuse may be destroyed.